(1) Field of the Invention
This invention relates to magnesium vapor discharge lamps useful as ultraviolet ray sources in photochemical reactions.
(2) Description of the Prior Art
Discharge lamps permitting effective emission of ultraviolet rays having wavelengths in the range of about 250-400 nm are used to induce photochemical reactions. High-pressure mercury vapor lamps and super high-pressure mercury vapor lamps, in each of which a discharge is produced between its electrodes, have conventionally employed as such discharge lamps. Furthermore, electrodeless high-pressure mercury vapor lamps have also been known recently, in each of which mercury and a rare gas are sealed in amounts sufficient to retain a discharge within an electrodeless light-emitting tubing, and electromagnetic waves such as high-frequency waves of several tens MHz or higher or microwaves are externally irradiated to the tubing so as to excite the internally-sealed mixture and to produce a discharge as light.
By the way, each of these electrode-type or electrodeless high-pressure mercury vapor lamps emits light having a line spectrum which comprises a number of peaks and extends over a considerably wide wavelength range. It is therefore inefficient to use high-pressure mercury vapor lamps for photochemical reactions, which require the above-mentioned range as an effective wavelength range. Accordingly, there are often employed metal vapor discharge lamps in each of which a metal halide is sealed as a light-emitting substance within the light-emitting tubing so as to increase the light quantity of a specific effective wavelength range. Magnesium vapor discharge lamps containing magnesium sealed therein can additionally output bright lines of 279 nm, 285 nm, 309 nm, 383 nm and 384 nm besides the spectrum of mercury. They are hence expected to improve the efficiency in improving certain chemical reactions.
However, the output of each of the above-described bright lines which have been newly given off owing to the sealing of magnesium is small compared with the output of the bright lines of the spectrum of mercury. Under the circumstances, the output of ultraviolet rays having wavelengths in the range effective for photochemical reactions, which a magnesium vapor discharge lamp gives off, is not substantially different from that of a high-pressure mercury vapor discharge lamp.